Toru Maruo

Characterization of the physico-chemical properties of environmentally friendly organic substrates in relation to rockwool

Summary Trials over two years aimed to characterize the physico-chemical properties and high-temperature responses of ecologically sound untreated organic substrates coconut (Cocos nucifera L.) coir and carbonated rice husk in relation to that of rockwool using tomatoes (Lycopersicon esculentum Mill.) as a test crop. In all substrates, water-filled pore space and water holding capacities were larger and air filled pore space was smaller. Bulk densities, water holding capacity and water-filled, air-filled and total pore spaces were lower in carbonated rice husk than coconut coir and rock wool. These values in coconut coir and carbonated rice husk were much increased with use. Most of the chemical properties, namely cation exchange capacity, electrical conductivity, pH, nitrate-N, P, K, Ca and Mg of these substrates were within recommended levels as growing media. There were no significant differences in plant height, stem diameter, individual fruit weight, percent fruit set, harvest index, ascorbic acid, total soluble solid, fruit pH, leaf chlorophyll contents, root dry matter percentage, fruit dry matter percentage and shoot/root ratio. There was less fluctuation in absolute growth rate, relative growth rate, net assimilate rate and leaf area ratio among the treatments. It also appeared that carbonated rice husk and coconut coir gave better crop performance and yield of tomatoes than rock wool under high temperature stress conditions namely 30°C and 35°C as compared with 25°C. Furthermore, crop productivity from the organic substrate coconut coir gave more profit than the popular rock wool. Thus, carbonated rice husk and coconut coir can be used successfully as a growing media amendment for producing fruit vegetables. .

Nighttime Supplemental LED Inter-lighting Improves Growth and Yield of Single-Truss Tomatoes by Enhancing Photosynthesis in Both Winter and Summer

Greenhouses with sophisticated environmental control systems, or so-called plant factories with solar light, enable growers to achieve high yields of produce with desirable qualities. In a greenhouse crop with high planting density, low photosynthetic photon flux density (PPFD) at the lower leaves tends to limit plant growth, especially in the winter when the solar altitude and PPFD at the canopy are low and day length is shorter than in summer. Therefore, providing supplemental lighting to the lower canopy can increase year-round productivity. However, supplemental lighting can be expensive. In some places, the cost of electricity is lower at night, but the effect of using supplemental light at night has not yet been examined. In this study, we examined the effects of supplemental LED inter-lighting (LED inter-lighting hereafter) during the daytime or nighttime on photosynthesis, growth, and yield of single-truss tomato plants both in winter and summer. We used LED inter-lighting modules with combined red and blue light to illuminate lower leaves right after the first anthesis. The PPFD of this light was 165 μmol m-2 s-1 measured at 10 cm from the LED module. LED inter-lighting was provided from 4:00 am to 4:00 pm for the daytime treatments and from 10:00 pm to 10:00 am for the nighttime treatments. Plants exposed only to solar light were used as controls. Daytime LED inter-lighting increased the photosynthetic capacity of middle and lower canopy leaves, which significantly increased yield by 27% in winter; however, photosynthetic capacity and yield were not significantly increased during summer. Nighttime LED inter-lighting increased photosynthetic capacity in both winter and summer, and yield increased by 24% in winter and 12% in summer. In addition, nighttime LED inter-lighting in winter significantly increased the total soluble solids and ascorbic acid content of the tomato fruits, by 20 and 25%, respectively. Use of nighttime LED inter-lighting was also more cost-effective than daytime inter-lighting. Thus, nighttime LED inter-lighting can effectively improve tomato plant growth and yield with lower energy cost compared with daytime both in summer and winter.

Crop Production and Global Warming

Crop production will be affected by global warming, resulting in world-wide food shortages and starvation. Increased concentrations of carbon dioxide (CO2), one of the main substances responsible for global warming, will promote plant growth through intensified photosynthesis. Some reports indicate that a rise in the levels of CO2 would actually benefit plants, rather than harm them. The growth rates of C3 plants increase in response to elevated concentrations of carbon dioxide. Thus, global warming might increase plant growth, because of higher temperatures and higher levels of atmospheric CO2. High atmospheric temperatures caused by elevated concentrations of CO2 will induce heat injury and physiological disorders in some crops, which will decrease the incomes of farmers and agricultural countries. Photosynthesis is one of the most sensitive physiological processes to high temperature stress. Reproductive development is more sensitive than vegetative development to high temperatures, and heat-sensitivity differs among crops. In tomato, the optimal temperature for fruit set was reported as 21–24°C (Geisenberg and Stewart, 1986) or 22–25°C (Peet and Bartholomew, 1996), while pollen viability and release are adversely affected by high temperatures, and become major limiting factors for fruit set. Thus, global warming can have opposite effects on plant growth. From a long-term viewpoint, however, high atmospheric temperatures will drive the main sites of crop production further north, establishing new rules for the ‘right crop for right land’. Water shortages caused by global warming will be the greatest problem for crop production. Plants fundamentally rely on adequate fresh water, and agricultural water accounts for 70% of water use world-wide. As higher temperatures increase evaporation from water sources and decrease precipitation, arid regions will become further desertified. Particularly in semiarid regions, the cultivatable area will decrease because of drought, and this could result in famines and mass migration. As well, it is likely that there will be human conflicts over irrigation water and food. Global warming is thought to be related to strong hurricanes, cyclones, and typhoons. These extreme weather events can seriously damage crop production, and destabilize farm management and the lives of consumers. However, these agricultural problems are most likely to occur in the medium and long-term future. In this chapter, we summarize some of the agricultural problems and crop damage that result from global warming, and present some technical countermeasures (not political and administrative countermeasures) that could be used to ameliorate the effects of global

Root Zone Cooling and Exogenous Spermidine Root-Pretreatment Promoting Lactuca sativa L. Growth and Photosynthesis in the High-temperature Season

Root zone high-temperature stress is a major factor limiting hydroponic plant growth during the high-temperature season. The effects of root zone cooling (RZC; at 25°C) and exogenous spermidine (Spd) root-pretreatment (SRP, 0.1 mM) on growth, leaf photosynthetic traits, and chlorophyll fluorescence characteristics of hydroponic Lactuca sativa L. grown in a high-temperature season (average temperature > 30°C) were examined. Both treatments significantly promoted plant growth and photosynthesis in the high-temperature season, but the mechanisms of photosynthesis improvement in the hydroponic grown lettuce plants were different between the RZC and SRP treatments. The former improved plant photosynthesis by increasing stoma conductance (Gs) to enhance CO2 supply, thus promoting photosynthetic electron transport activity and phosphorylation, which improved the level of the photochemical efficiency of photosystem II (PSII), rather than enhancing CO2 assimilation efficiency. The latter improved plant photosynthesis by enhancing CO2 assimilation efficiency, rather than stomatal regulation. Combination of RZC and SRP significantly improved PN of lettuce plants in a high-temperature season by both improvement of Gs to enhance CO2 supply and enhancement of CO2 assimilation. The enhancement of photosynthetic efficiency in both treatments was independent of altering light-harvesting or excessive energy dissipation.

Lettuce production using a commercial scale recirculated capillary hydroponic system

Three experiments were carried out sequentially in spring, summer and fall to study the possibility of producing butterhead lettuce (Lactuca sativa L.) using a capillary hydroponic system (CHS) on a commercial scale under tropical environmental conditions. In all the experiments, two temperature regimes combined with two flow rates of nutrient solution were applied. The air temperature was controlled in the ranges of 25-30•Ž and 30-35•Ž and the solution flow rates were 50 or 80 ml•Emin-1•Em-1. For all the three growing seasons, better plant growth was associated with the lower temperature regime. Higher water flow rate stimulated plant growth only in the summer growing period under the higher temperature regime, due to the larger amount of dissolved oxygen in the nutrient solution. Although the plant quality parameters and leaf color remained unaffected under most of the temperature regimes and flow rates, they differed according to the seasons. In general, higher SPAD values and nitrate concentrations were observed in the spring and fall growing seasons as well. Lower SPAD values and higher vitamin C concentrations were recorded in the summer growing season. The estimated cost of the required-materials for constructing a 1000m2 CHS in Paraguay and Thailand amounted to \665,950 and \659,100 respectively, based on the price of the materials in each country. Estimated cost of the materials in Japan was threefold higher than that in the tropical countries. All the year round lettuce production under tropical conditions using CHS was considered to be fairly possible, since the microclimatic conditions in the greenhouses were similar to those of outdoor tropical conditions.

Evaluation of Lettuce Cultivars Suitable for Closed Plant Production System

There are many cultivars in butterhead lettuce (Lactuca sativa L.) and if some of them can perform well in the relatively low light and high temperature condition, the commercial lettuce production become feasible because of the lower electric consumption in the plant factory. Eighteen cultivars were grown in the summer greenhouse under 50% shading condition, and the growth indices of seedling stage were examined in relation to the quality of final products (Expt.l). These cultivars were classified into two groups, namely unsuitable (lower qualities) and suitable (higher qualities). The ratio of leaf length to width and chlorophyll content in the seedling stage closely related to the quality of the final products. Twelve cultivars of both groups were selected from the previous experiment and grown in a closed production system to evaluate the productivity and the quality (Expt.2). The performance of the plants showed a similar tendency with those under the greenhouse condition. Thus, the ratio of leaf length to width and chlorophyll content in the seedling stage were found to be an effective index for the evaluation of the performance of lettuce cultivars.

Effective Vegetable Transplant Production Programs for Closed-Type Systems Under Different Lighting Regimes

Since the high cost of electricity can limit the viability of artificial environment growing facilities, recent research has focused on the development of energy efficient lighting systems to reduce costs. In facilities designed for transplant production, however, reducing electricity usage per se is not enough to improve productivity. If plant growth can be increased and harvest stage reached more rapidly, both the fixed property cost per plant and the total production cost will decrease even if energy cost per plant remains constant. The present experiments test whether transplant production efficiency can be increased by shortening dark period length while maintaining a constant light period. Light treatments were initiated after cotyledon emergence in three crops (lettuce, cucumber and tomato). Light period was set at 10 hours in all regimes, while dark periods were set at 0, 2, 6, 8, or 14 hours. Lettuce plants grew faster with decreasing dark period length, requiring only 10 days to reach 1.2g in the 10:0 light/dark treatment, compared with 10, 13, and 17 days in 10:2, 10:8, 10:14 treatments, respectively. However, it should be noted that the 10:8 and 10:14 treatments received the approximately the same number of hours of light prior to harvesting. In contrast, shortening dark period length did not improve growth rates significantly in the tomato and cucumber plants, presumably because chlorosis occurred as a result of the shorter dark period. The facility efficiency can, therefore, be improved by shortening dark period and thereby promoting faster growth in some plants.